Resin transfer molding (RTM) is a well known method of producing large composite structures, such as vehicular bumpers and the like. According to present RTM technology, two liquid components, a resin and a hardener, are mixed together and immediately transfer through a supply line to a shut off valve located immediately upstream of a sprue leading into the mold and ultimately to a mold cavity. Once the mold cavity has been filled, the valve is closed and the supply line detached from the valve. The entire mold, sprue and valve assembly is then heated to a curing temperature so that the mixed resin solidifies around the reinforcing matrix to form a rigid and durable product. The mold is then opened and the product removed from the mold cavity. However, before the mold can be cycled again, the cured resin must be removed from the sprue and valve assembly.
Because the resin material, once cured, is extremely hard and adheres steadfastly to all contacting surfaces, the sprue and valve assembly frequently becomes clogged with a cured residual core of resin. Because the prior art has not found a more efficient method of removing the cured residual core from the flow passage in the sprue and valve assembly, the prevalent technique for cleaning the sprue and valve assembly is to drill out the cured residual core. Thus, according to the most advanced prior art techniques, the sprue and valve assembly must be cleaned of the cured residual core between each cycle of the mold by drilling out the cured residual core.